Blood Supply of the Posterior Shoulder

The Scapular Arcade and Collateral Flow

One of the most clinically significant features of the shoulder's vasculature is the scapular arcade. This is a series of arterial anastomoses formed by the interconnection of the branches mentioned above.

The arcade essentially creates a loop of blood vessels that links the subclavian artery system with the axillary artery system. This arrangement provides a mechanism for collateral blood flow.

Clinical Note: Collateral Circulation In cases of slow occlusion of a major vessel, such as the axillary artery, the body can utilize the scapular arcade to develop sufficient collateral flow. This helps prevent ischemia (lack of blood flow) to the surrounding tissues of the arm and shoulder.

Vascular Gateways and Clinical Correlations

The various arteries of the posterior shoulder must pass through specific anatomical "gateways" to reach their targets. These spaces are often sites of clinical importance where nerves and vessels may become compressed.

The Quadrangular Space

The quadrangular space is a vital passage located between the teres minor (superiorly) and the teres major (inferiorly), with the long head of the triceps forming its medial border and the surgical neck of the humerus forming its lateral border.

Its primary contents are the axillary nerve and the posterior circumflex humeral artery.

Clinical Connection: Quadrangular Space Syndrome Hypertrophy of the muscles surrounding this space or fibrosis can lead to "Quadrangular Space Syndrome." This can compress both the axillary nerve (causing deltoid weakness and teres minor atrophy) and the posterior circumflex humeral artery. Patients may present with diffuse posterior shoulder pain and lateral arm paresthesia (tingling).

The Triangular Space and Triangular Interval

Other important pathways include:

• Triangular Space: Located between the teres minor, teres major, and the long head of the triceps. It contains the circumflex scapular artery and vein.
• Triangular Interval: Bound by the teres major, the shaft of the humerus, and the long head of the triceps. This space transmits the radial nerve and the profunda brachii artery.

The Suprascapular Foramen

Finally, the suprascapular foramen (formed by the transverse scapular ligament) serves as a route for structures passing from the base of the neck to the posterior shoulder.

Exam Tip: "Army over Navy" To remember the contents of the suprascapular notch, use the mnemonic "Army over Navy": the suprascapular artery passes over the ligament, while the suprascapular nerve passes under it.